This study will evaluate the effectiveness of pioglitazone, a new diabetes medicine, on decreasing insulin resistance and improving liver disease in patients with nonalcoholic steatohepatitis (NASH). NASH is a chronic liver disease with unknown cause that involves fat accumulation and inflammation in the liver, leading to liver cirrhosis in 10 to 15 percent of patients and significant liver scarring in another 30 percent. Although similar to a condition that affects people who drink excessive amounts of alcohol, NASH occurs in people who drink only minimal or no alcohol. It is most often seen in patients with insulin resistance. Pioglitazone decreases insulin resistance and improves blood lipid (fat) levels, so that it may improve liver disease in NASH.